Fine needle aspiration biopsy (FNAB) has been shown to be an accurate method for evaluation of palpable breast masses; however, it has been used infrequently for evaluation of nonpalpable lesions because accurate needle placement is difficult. The recent development of a stereotactic mammography system allows precise localization of mammographically suspicious lesions with the biopsy needle and localizing wire. This study will evaluate 100 women with nonpalpable mammographic abnormalities who are referred for needle localization prior to open surgical biopsy. Utilizing a stereotactic guidance system, FNAB specimens will be obtained prior to the placement of the localizing hookwire. Preoperative hookwire localization will direct surgical excision of the lesion, which will be additionally localized within the surgical specimen by means of specimen radiography and needle placement. This second localization will ensure histologic evaluation of the radiographically abnormal area. FNAB cytology and surgical tissue histology will be compared and statistically analyzed. This study will allow determination of 1) the efficacy of the stereotactic system from needle localization and FNAB, and 2) a comparison of FNAB cytology and surgical specimen histology in the evaluation of nonpalpable mammographically demonstrable lesions. The recording of health care costs in the study will allow estimation of the monetary savings afforded by the possible elimination of the surgical biopsy and will also permit projection of the potential savings to the national health care system.